The present invention relates to methods and apparatus for modifying an intercondylar area of a patient's femur in order to prepare same for receiving a knee prosthesis.
There are a number of different categories of prosthetic knee systems that are used in total knee replacement surgery. Among these categories is the posteriorly stabilized prosthetic knee system, where the posterior cruciate ligament is either weakened or non-present due to injury or disease, or where the posterior cruciate ligament is sacrificed during the knee replacement procedure itself.
FIG. 1 illustrates a knee that has been repaired using a known posteriorly stabilized prosthetic knee system 10. The system 10 includes a posteriorly stabilized tibial bearing component 12 and a posteriorly stabilized femoral component 14, which are coupled to the patient's tibia 16 and femur 18, respectively. The femoral component 14 is slotted (including a cam 21, not shown) and the tibial bearing component 12 includes a post 20. The post 20 extends into, and is engaged by, the slot of the femoral component 14 in order to provide both movement and stability of the knee joint.
In order to provide clearance for the cam 21 of the femoral component 14, the post 20 of the tibial bearing component 12, and in some designs a box of the femoral component 14, the intercondylar area of a patient's femur 18 must be modified. Otherwise, the cam 21, post 20, etc. would interfere with the biological structures of the patent's femur 18, and the patient would not enjoy a full range of motion. The bone around the trochlear groove and the intercondylar notch of the distal femur 18 is highly loaded and is, therefore, some of the hardest bone in the body. Some of this very hard bone must be removed in order to provide the aforementioned clearances.
There are a number of known methods to remove the intercondylar bone in preparation for a posteriorly stabilized knee prosthesis system. Perhaps the most common method is to use a notch preparation guide, which includes a series of surfaces to guide a sagittal saw. This technique for preparing the intercondylar notch is described in U.S. Pat. No. 6,503,254, the entire disclosure of which is hereby incorporated herein by reference. The surfaces of the notch preparation guide permit the use of one or more sagittal saws to form three resections at right angles to each other. The three resections leaves a box-shaped intercondylar region, notably with sharp square corners. These sharp corners lead to concentrated bone stresses and the significant possibility of femoral fracture. In some cases, the corners are overcut, where the saw violates the adjacent resection, leading to a very high stress concentration. This method also leads to an excessive amount of bone being removed from the intercondylar area. The more bone that is removed, however, the more likely it is to: (i) compromise the integrity of the modified structures of the femur, and/or (ii) compromise the recovery of the patient.
Another known technique to remove the intercondylar bone in preparation for a posteriorly stabilized knee prosthesis system is described in U.S. Pat. No. 5,769,854, the entire disclosure of which is hereby incorporated herein by reference. In this technique, a notch preparation guide and a punch are used to remove the intercondylar bone. Using a punch and notch-preparation guide is considered an improvement over the sagittal saw because the shape of the box can be better controlled and it takes less time to use a punch than it does to make three saw cuts. As mentioned above, however, the intercondylar bone is very hard and can be very difficult to punch. More problematically, however, is the fact that the punch may result in small or large cracks in the remaining bone of the distal femur. Such cracks may be apparent at the time of surgery or may represent latent damage. In either case, the punch technique may lead to high stress concentrations (at sharp corners and/or cracks), excessive bone removal, a compromise of the structural integrity of the modified femur, and/or limited recovery of the patient.
Yet another technique for preparing the intercondylar notch to receive a posteriorly stabilized total knee system is described in U.S. Pat. No. 4,721,104, the entire disclosure of which is hereby incorporated herein by reference. This technique calls for a notch preparation guide, which guides an end mill to remove the bone from the intercondylar notch. While using a milling device and a notch preparation guide may provide some improvement in the notch preparation, there is a significant disadvantage. The milling device allows for a powered mill to be used to remove the bone from the intercondylar notch. The milling cutter does not result in one or more discrete pieces of bone that may be readily collected and used for other purposes (such as to fill in the intermedullary hole made for femoral alignment). Rather, the milling device creates a “dust” that is relatively useless.
In view of the above, there are needs in the art for new methods and apparatus for preparing an intercondylar area of a patient's femur in order to receive a knee prosthesis. Among the desired characteristics of such new methods and apparatus are the ability to: (i) yield a modified intercondylar notch that exhibits an arch shape (with no sharp corners) in order to achieve structural strength, (ii) remove a relatively low or minimal amount of bone from the intercondylar notch, and (iii) collect discrete bone (preferably one piece) from the intercondylar notch such that the bone may be used for other purposes during or after the knee replacement surgery.